76 London Institution, 



about 100 miles eastward of the Cumberland coal-measures before 

 described. They occur at Dickson's mills, \\ mile west of Pictou, 

 in a bed of sandstone about ten feet thick. They all terminate 

 downwards at the same level where the sandstone rests on subjacent 

 limestone ; but the tops are broken off at different heights, and 

 Mr. Dawson observed in the same bed a prostrate Lepidodendron, 

 with leaves and Lepidostrobi attached to its branches. 



From the facts above enumerated, Mr. Lyell draws the following 

 conclusions : — 



1 . That the erect position of the trees, and their perpendicularity 

 to the planes of stratification, imply that a thickness of several thou- 

 sand feet of coal strata, now uniformly inclined at an angle of 24°, 

 were deposited originally in a horizontal position. 



2. There must have been repeated sinkings of the dry land to 

 allow of the growth of more than ten forests of fossil trees one above 

 the other, an inference which is borneoutbythe independent evidence 

 afforded by the Stignnaria, found intheunderclays beneath coal-seams 

 in Nova Scotia, as first noticed in South Wales by Mr. Logan. 



3. The correspondence in general characters of the erect trees of 

 Nova Scotia with those found near Manchester, leads to the opinion 

 that this tribe of plants may have been enabled by the strength of its 

 large roots to withstand the power of waves and currents much more 

 effectually than the Lepidodendra and other coal plants more rarely 

 found in a perpendicular position. 



Lastly, it has been objected, that if seams of pure coal were formed 

 on the ground where the vegetables grew, they would not bear so 

 precise a resemblance to ordinary subaqueous strata, but ought to 

 undulate like the present surface of the dry land. In answer to this 

 Mr. Lyell points to what were undoubtedly terrestrial surfaces at 

 the South Joggins, now represented by coal seams or layers of shale- 

 supporting erect trees, and yet these surfaces conform as correctly 

 to the general planes of stratification as those of any other strata. 



He also shows that such an absence of superficial inequalities, 

 and such a parallelism of successive surfaces of dry land, ought to 

 be expected, according to the theory of repeated subsidence, be- 

 cause sedimentary deposition would continually exert its leveling 

 action on the district submerged. 



LONDON INSTITUTION. 

 December 18, 1843. — Professor Grove on the Correlation of Phy- 

 sical Forces. Mr. Grove has just finished a course of six lectures 

 on the above subject, commenced November 13. The object of the 

 course has been to show that motion, chemical affinity, heat, light, 

 electricity and magnetism are all convertible affections of matter, — 

 that either being taken as an initial mode of force is able to produce 

 any of the others ; thus moving bodies may be made mediately or 

 immediately to produce heat, light, electricity, chemical affinity, or 

 magnetism. Matter affected by chemical affinity may be made to 

 produce motion, heat, light, electricity and magnetism, and so of the 

 rest. 



